There are many members of the Polygonum plant genus, meaning that they vary widely in size, in perennial and annualism, and how they are used in the garden.
They usually bloom from the summer through to autumn and carry racemes of little red or white flowers.
The range in size and nature of Polygonum means that they can be used in many parts of the garden; however many members are aquatic and so can be used in boggy parts of the garden or in water features.
Some common names for Polygonum include Knotweed, Bistort, Russian Vine, Vietnamese Coriander, Smartweed and Prince's feather.
Polygonum multiflorum (Tuber fleeceflower / Chinese climbing knotweed / He shou wu), photograph by 阿橋 HQ; CC.
Polygonum cuspidatum (Japanese knotweed / Asian knotweed), picture by Matt Lavin; CC.
Common Names: Knotweed, Bistort, Wiregrass, Tear Thumb, Knotgrass, Arssmerte, Mile a Minute, Smokeweed, Swamp Smartweed.
Life Cycle: Half hardy annual, hardy annual. Half hardy perennial, hardy perennial.
Height: 2 to 135 inches (5 to 350 cm). Vines may grow up to 100 feet (30 M).
Growing Region: Annuals: zones 3 to 10. Perennials: 3 to 9.
If growing outdoors from the off then it is best to sow Knotweed and other Polygonum species outside just after the last frost of spring; once sown lightly cover the Knotweed seeds with topsoil.
The plants prefer to grow in a partially shaded part of the garden and like to have a moist soil of pH 6 to 7.5.
Even though the soil should be moist it is important that Knotweed grows in areas of good drainage.
If starting Polygonum indoors then do so about three weeks before you expect the last frost.
The seeds can take anything from 3 to 8 weeks to germinate at a temperature of 21 to 24 degrees centigrade (70 to 75°F).
Once ready, transplant the seedlings at a spacing of 20 to 30 cm (8 to 12 inches) for small Polygonum species; 30 to 60 cm (12 to 24 inches) for medium size; or 70 cm to 1.2 m (30 to 48 inches) for larger Polygonum varieties.
Knotweed and other Polygonum plant genus members like to grow in a moist garden soil, so keep well watered.
The vine varieties of Polygonum should be pruned heavily at the start of spring to prevent scrawny growth and to make them more attractive.
Once flowering has finished, cut back the stems (usually in the autumn).
If you require more plants then they can be propagated by division in the autumn.